After drilling one of each pair of seat belt anchors, the instructions have you clamp a 3/16 shim between the pair to align them before match drilling the second of the pair. My bright idea was to use a piece of scrap 3/16" aluminum left over from lightening the control stick mounts. It turns out that this angle is about 0.01 thicker than 3/16, and anal me wouldn't let that slide. I had already spent an inordinate amount of time trying to thin that scrap of aluminum when in dawned on me to clamp a 3/16" drill bit at the base, and 3/16" worth of washers at the seat belt fitting attach hole. Voila! One pair down, three to go. Then they'll have to be trimmed to clear the seat ribs...
Seat belt anchors shimmed, aligned, and clamped to each other.
Seat belt anchor pair bolted, squared, and clamped to the bulkhead for match drilling.